Coated superconducting material is one of the high-temperature superconducting materials with broad application prospects and great potential commercial value. In a textured metal substrate used for coated conductors, since the core of the composite substrate is made of high-strength, non-ferromagnetic alloy material, the mechanical and magnetic properties of the entire composite substrate with high cube textured surface are further improved, so that the composite substrate is one of the new metal alloy substrates with high performance and high potential application value. Element diffusion composite substrate has been proven to be a high performance textured metal substrate used for coated conductor, which has the capability to obtain sharp cube texture and has a good interface binding force between the inner layer and the outer layer.
Currently, Ni—W alloy substrate is one of the most widely studied substrate materials in scientific research. Compared to smelting method, it is easier for powder metallurgy method for preparing a composite substrate to achieve interlayer element diffusion. In addition, the recrystallization temperature in the powder metallurgy method is much higher than that in the smelting method, and thus the powder metallurgy method has more pronounced diffusion effect than the smelting method. Hot isostatic pressing technique is more suitable for preparing large billets to achieve large scale industrial production of composite substrates. But exorbitant annealing temperature will deepen the depth and width of thermal erosion grooves, which is unfavorable to further coating a transit layer on the surface of the composite substrate. In view of this, powder metallurgy method is taken in the present invention for preparing element diffusion composite Ni—W alloy substrate. By using electric pulse technology, a high-frequency and low-voltage large pulse current is passed through a substrate being annealed in the furnace in the process of dynamic annealing, which thereby greatly enhances the interdiffusion of interlayer elements in the composite substrate and reduces the recrystallization temperature of the substrate to some extent.
In the aspect of liquid metal solidification, the pulse current treatment leads to increase in metal solidification temperature, decrease in solidification time and temperature gradient, solidification structure refinement and mechanical property improvement; in the aspect of solid metal element diffusion, electric pulse technology can enhance diffusion coefficient and reduce diffusion annealing temperature. Reduced energy consumption-during high temperature annealing can reduce costs. In addition to enhancing the interdiffusion effect of interlayer elements of the composite substrate, the main effect of high-energy electric pulse is due to the interaction between electrons and dislocations, which can greatly enhance the process of recrystallization of the alloy, but it just promotes recrystallization nucleation in the deformed tissue and has no significant effect on the mechanisms of nucleation in deformed band and the final texture of composite substrate.
In summary, sandwich-like Ni—W alloy composite substrate prepared with the powder metallurgic method is more favorable to interdiffusion of interlayer elements, by which higher concentration W sufficiently diffuses from the inner layer to the outer layer, leading to the ferromagnetic character of the entire composite substrate being weakened. Electric pulse accelerates element diffusion effect of the composite substrate, meanwhile improves the surface roughness of the composite substrate indirectly, so that the general application performance of the composite substrate is further improved.
The method according to the present invention can be applied to large-scale production of high-performance composite substrate by a vertical dynamic annealing device.